Analog circuits such as differential, common source or common drain or common gate amplifiers can be used to provide an abundance of functions ranging from a unity gain amplifier to a high frequency gain amplifier. Due to the demand for low-power integrated circuit (IC) chips, these particular analog circuits, in certain conditions can be disabled in order to eliminate or reduce the constant direct current (DC) consumption that is expended when active. This concept can be referred to as sleep mode. When these circuits are once again enabled or brought out of sleep mode, it is desirable that the analog circuits supply a stable output reference voltage as quickly as possible.
FIG. 1 is a conventional unity gain amplifier circuit 100 which is one of the many conventional solutions that may be used, where part of a first stage differential amplifier 102 supplies a bias voltage to a common source amplifier 106 of a second stage 104. When the circuits 102 and 104 are disabled (in sleep mode), the amplifier 100 is not conducting any current other than leakage current. When amplifier 100 is enabled from sleep mode by a sleep-bar signal 103, it is desirable that it recovers to provide a stable reference output voltage signal 110 as fast as possible. However, with compensation feedback implemented, which limits the recovery of the first stage differential amplifier 102, the amplifier 106 relies on the source/sink capability of the differential amplifier 102 to provide a fast recovery. In cases where increasing the current consumption capability is not feasible, a slow recovery of output reference signal 110 is realized.
A conventional technique of sleep recovery is to increase the source/sink capability of the differential amplifier 102 in order to meet the sleep recovery requirements. In other words, the conventional solution to this problem is to rely on the differential amplifier 102 to supply an output 108 with a stable voltage level 110 which results in higher current consumption for faster recovery from sleep mode.
One of the disadvantages associated with this conventional solution is that in order to meet sleep recovery specifications at low voltage and/or low-power situations, the differential amplifier 102 is designed for faster turn-on, which directly correlates to more current consumption, which may not be feasible in low-power applications. Additionally, this can lead to an area increase as well.
It would be desirable to have a solution that does not have the disadvantages of the conventional solution.